BENCH BLOG (October 2020)

Out of lockdown, Tim Hooper heads for the flying field to test fly some recent new builds and refurbs.

Flying wise it was a no-go for several weeks. Our field was shut, just as you’d expect when the weather turns gloriously sunny. Yes, I know that it would be possible to maintain the required social distancing on the flight line, but the clubhouse and pits could be problematical, and it simply wasn’t worth the risk.

So, what to do in this unlikeliest of global scenarios? There were three models that still awaited maiden flights since being completed last year. First, there was the Keil Kraft Ladybird electric free-flighter; second, the diesel-powered Antares38 aerobat and, third, that Bird of Time inspired glider, the Sunbird. All were ready and eager to go for some weeks but had to await their moments of glory in my new hangar for the moment.

So, let’s kick off this column by back-tracking to last autumn for a minute or two, by finishing the tale of my down-scaled Antares aerobat.

ANTARES 38

You might recall that the new, smaller Antares was inspired by my old brown bruiser that succumbed to glue fatigue whilst on an inverted low pass. The new baby is a 70% re-size and is equipped with the very latest in motive power tech in the shape of a 1.5cc PAW diesel engine. Let’s get back to the plot.

After waiting patiently for several months, the little Antares38 finally made its first foray to the newly reopened club field for engine testing, and the tempting possibility of a first flight if everything went well.

Our club boasts a small, fenced off area that’s set aside for tethered engine fettling, so the Antares38 was tied down to a dog spike and fuelled up. Given that the model only has room for a 2oz tank, I’ve found that it’s a simple matter to use a 20ml syringe, equipped with a fuel tube extension, to load up the tank with a couple of squirts of fuel.

The PAW 1.49 hadn’t been run for several months and had dried up a little, so a splash into the air intake, followed by several turns of the prop, freed it up nicely. I’d already run the engine on a test bench previously and had developed a sort of regimen to allow easy starting; fuel up, finger choke and turn over to fill the feed pipe, a quick prime and then a few flicks to start it.

Now, that’s all very well when you’re working at a waist high bench in the garden. But it’s different when the installed engine is cowled into the nose of a model that is sat on the ground, as any IC man will tell you.

Well, I flicked and primed repeatedly, flooded the engine, backed off the compression, flicked it dry, primed again, increased the compression, etc. Yes, it fired and ran briefly, then it backfired and stopped. All very frustrating. It would only fire and run if the compression was backed off so far that it died before I could get behind the prop to increase the compression to keep it running.

I know that all of this is nursery stuff to the senior diesel hands out there, but I was knelt on the ground, complete with aching back and knees, for some time before the engine actually kicked and ran properly. Not one to miss an opportunity, and given the emptiness of the flight line, I grabbed the transmitter and the idling model, and headed directly for the pilots’ box.

Pointing the Antares into wind (there’s no steerable nosewheel, remember), I gently pushed the throttle open and was delighted to find that the model tracked pretty straight as it barrelled along the strip. A touch of up and we were away, at last!

Just a single flight that day but one that included a few obvious elements, including a stall test (benign) and a hands-off dive test to check the CG (just about right). Oh, and a loop and roll to make sure I could still remember how to fly a toy aeroplane after all those weeks of home rule.

After five minutes or so I throttled back for a landing and brought the model in reasonably smoothly. I was able to taxy it back towards the vacant flight line, furtively juggling the elevator, rudder and throttle controls to maintain steerage on the ground.

The Antares’ second outing was scheduled as a photo shoot. Gyromeister, Rich Harris accompanied me on a glorious May afternoon to a suspiciously empty club field, so we could get some pics of several models. The gusty breeze was warm in the blazing sun.

Again, the little PAW in the Antares proved hard to start. Rich has subsequently put together a video montage of the afternoon’s flights, just to show the funny side of the whole procedure:

Two more flights were eventually completed. In the air the scaled down model is great; the enlarged ailerons and rudder are proportionately more effective than on the original, larger Antares and it grooves really nicely.

The little PAW is never going to provide great surges of power to allow never-ending verticals, but there’s plenty of momentum available for largish loops and bunts. Rolls are quite rapid, albeit a tad barrelly.

The engine seems to be pretty reliable in the air and throttles back reasonably well, although if it’s allowed to cool too much it will tend to falter and quit, which is par for the course, I’m told. But still, there’s the problem with achieving a reliable start-up procedure. I mean, it was fine on the bench, wasn’t it – even with the engine sidewinder mounted? Back at home, I hit the internet for suggestion to affect a cure…

TANK POSITION

I stumbled across a video, produced by PAW themselves, and the very first thing mentioned was tank position. If the tank is too high then you get all the symptoms that I’d been suffering due to the engine continually flooding when the tank is full and the fuel level is above the spray bar. Obvious really, when you think about it.

Now, if I’d obeyed protocol and mounted the engine vertically the spray bar would, by default, be above the level of fuel when the tank was full. But, because Clever Clogs here had laid the engine on its side then the spray bar is always going to be drip-fed when the tank, sited on the centreline, is full.

This isn’t a problem when the engine is running, just when it’s sat on the deck. It’s not possible to lower the tank in the Antares’ skinny nose, so we need to find an alternative solution.

Most brutally, there’s the option of sawing the nose off, re-fitting the engine in an upright position and then re-building the cowl – and throttle linkage, fuel feed, etc.- which is not a job I’d relish, if only because it would spoil the Antares’ sleek side profile.

The other option is to forego starting the model on the ground and go all control line by holding the model in the hand at a 90° angle, with the cylinder pointing skywards. Whether this is possible to do solo is questionable safety-wise to my mind. But then, if this were a free flighter, it would be normal practice, wouldn’t it?
To be continued sometime…

MORE SUPER SCORPION

You might recall that a few issues ago I was smugly blithering away about my re-born Super Scorpion. I’d built the model over 15 years ago and powered it with a (then) state-of-the-art Astro15 brushed electric motor, powered by 12 huge sub-C NiCads.

The custom-shaped packs lived their life out and then the big Scorp found its way to the back of the hangar for a few years. Eventually it was hauled back into the light and given a new 3S LiPo battery. Not content with that, I ventured into higher-voltage territory and fitted a 4S 4000mAh instead. The difference in climb rate was little short of remarkable, although the old-school geared motor was making a noise like a deranged banshee.

Well, shortly after the last episode was published the motor’s ancient drive pinion gave up the ghost and shed its oily bronze teeth generously over the inside of the Scorp’s fuselage, and the model was taken back the workshop for some appropriate rumination. The Astro15 was toast and needed replacing, that much was clear.

Back at home I dug out another Astro motor, this time a smaller 05 model, which looked quite promising, but which was rejected as being not quite up the job. Rooting through my stock of old motors I stumbled upon an E-flite 15 outrunner, which I reckoned would do the job admirably. This motor came out of a dead Pulse15 ARTF and was originally designed to spin a 12 x 8 prop on 3 cells. However, I know from experience that it’s happy to run on four cells, as long as the prop load is reduced by fitting an 11 x 7 prop instead, and that there’s plenty of airflow over the 40-amp ESC.

Now, the E-flite 15 is a lot shorter and lighter (by some 3oz) than the extinct Astro lump. Not only that, but the motor was set up for reversed fitting, with the shaft protruding from the rear of the bell casing. Releasing the grub screws that secured the shaft in the bell let me push the shaft through, using a vice, so the shaft came out of the mounting flange end instead. Easy-peasy.

The firewall needed to be re-drilled for the four bolts to mount the motor and the easiest way to access the firewall was to slice off the outer balsa nose block that was glued to the front of the firewall. The supplied aluminium X-mount that was fitted to the outrunner was unscrewed and binned, to maximise the length of the output shaft. Once again, the gubbins box received a severe rooting to find a suitable prop adapter.

Uncharacteristically thinking ahead, I epoxied a 3oz billet of lead in the nose, to make up for the reduced mass of the new motor. The original Jeti 350 (brushed) ESC was honourably retired and a 40A Turnigy item used to replace it.
With the motor removed again, I made up a new balsa nose block, which was shaped and covered in deep red film to replace the old nose, to maintain the overall look of the model.

Job done, and the big Scorp was taken back to the field and put to the test. Just to make a comparison, in its original NiCad powered guise the Scorpion used to trundle across the grass for twenty yards or so before leisurely nudging itself into the air. That’s all changed and now we can get airborne in half that distance and go straight into a 45° climb out. Mind you, that sort of launch looks a bit ugly and out of character, so it’s prettier to take off at half throttle and then ease back a bit once the wheels are clear of the strip. Flight times on the 4S 4000mAh are long and I get a bit bored after 20 minutes, I’m almost ashamed to say.

So, once again, one of my favourite elder models has had second mild refurb and, hopefully, a new lease of life for the coming years. It’s still a pleasure to fly and is one of the prettiest models in the fleet, so I’d like to keep it functional for a long time to come.

MOTIVE POWER

Solely because I’ve been a very good lad in recent months, I decided to award myself some nice new LiPo packs for the existing fleet. Over the years I’ve bought new packs piecemeal, as and when I needed them. Being congenitally idle, I’ve just kept the old, knackered packs on a shelf and not bothered to dispose of them properly. Shame on me.

Previously, my packs have been bought from a variety of cut-price suppliers, either online or at shows, and they’ve either puffed or failed over time. That’s probably due to my atrocious habit of storing them fully charged, which, apparently, is a bad idea. On the other hand, I’ve never had a pack fail suddenly. Neither have I ever had a pack catch fire, either on the ground or after a really bad crash. Believe me, I’ve tried really hard, too!

The decision was made to rationalise my needs as well. Since I field-charge from a couple of whopping great caravan batteries as I go along, I don’t need to have six of every LiPo size I use to last through the flying session. In practice, a couple of each type will suffice quite nicely, thank you very much.

I thought I’d try a new vendor, so I placed my online order with George Worley at 4-Max, a firm I’d not purchased from before. I received a call from George himself, to confirm a couple of details, which I thought was indicative of great service. I’ll let you know how the new cells perform as time passes.

INDICATOR BULBS

However, this new situation left me with a whole tranche of over twenty packs to discharge and then dispose of. My chargers all feature a discharge function as normal, but they’ll only discharge a pack down to 3V per cell, and I wanted to discharge each pack down to zero.

Shorting them out through the connectors was obviously going to be a no-no, being potentially explosive and dangerous, so I needed a way of letting them down gently, without causing too much emotional trauma to the poor things.
This isn’t a new idea, by any means, so stop me if you’ve heard it before.

Remember when motor cars were fitted with conventional light bulbs at their corners, before the automotive world adopted the LED as a matter of course? Well, those 21 watt indicator bulbs lend themselves to a new life as Weapons of Discharge for dead LiPos.

I rummaged around in the Brown Cupboard and found three spare bulbs. Out came the soldering iron and fly leads (sporting my favourite 4mm connectors) were attached to each bulb, all ready for use.

Now, a single 12V 21 watt bulb is happy to discharge either a 2 or 3 cell LiPo without demur, and will also do the business on a 4S pack that’s already been discharged down to 12V. However, killing a big 5S pack takes two bulbs, wired in series, to do the job. To be fair, this is quite a lengthy process. There’s a lot of residual grunt inside a hefty 5S pack, so it took several hours to reduce the voltage to the required one volt per individual cell.

Don’t be fooled that the job is finished when the bulb ceases to glow as there are still quite a few electrons knocking about that need to be quashed permanently, so keep it connected until a voltmeter confirms end of life. Oh, and it goes without saying that the above process all took place in the middle of the patio, well away from anything combustible.

Right then, let’s get connectors attached to those new 4-Max packs and see how we get on!

MOVING ON

Our new address has called for a new workshop, obviously. After a bit of domestic negotiation, I’ve been granted the run of the large conservatory as a new playroom. I’ve plumped to use an old office desk as my new building bench in one corner, whilst behind me is an existing kitchen type worktop and drawers, which now serve as a base for my major vice. The other, seldom used, power tools reside on another bench inside the garage/hangar.

I’ve organised supplemental lighting over the bench, six electric sockets and a hefty fan heater below for when the nights turn chilly. What I’m missing is the old set up for taking studio type photos against a plain white backdrop, so we’ll see how we get on with using the desk itself. Mind you, there’s been a couple of comments on the model flying fora recently asking for more everyday realism in the mag’s photos, so this could be the ideal opportunity to make a change for the simpler.

We’ve also been blessed with a generous garage and I’ve claimed the back wall for hanging hangarage.